1. Field of Invention
The present invention relates to a photosensitive resin composition, a spacer or a protective film formed by the aforementioned photosensitive resin composition, and a liquid crystal display device (LCD) including the aforementioned spacer or protective film. More particularly, the present invention relates to a photosensitive resin composition having excellent resolution and development adherence, a spacer or a protective film formed by the aforementioned photosensitive resin composition, and a LCD including the aforementioned spacer or protective film.
2. Description of Related Art
In general, uneven surfaces generated from color-printed pixels and black matrixes on the surface of a color filter layer can be covered with a protective film thereon the surface of the color filter layer for planarization.
However, during manufacturation of optical devices such as liquid crystal display devices or solid state imaging apparatus, there have to be treated by some processes under severe conditions. For example, a wiring electrode layer can be formed on a substrate surface by various methods of treating the substrate surface, for example, immersing the substrate surface into an acid solvent or alkaline solution, being sputtered on the substrate or the like. Such severe treatments can cause local corrosion or local high temperature. Therefore, it is necessary to cover protective films on the surfaces of these devices, so as to avoid the devices from being damaged during the manufacturation. In order to enable the protective film to resist damages of the aforementioned treatments, the protective film must have excellent adhesion to the substrate, as well as a surface with a high transparency, a high surface hardness and smoothness. Moreover, a protective film with high heat resistance and light resistance will not be deteriorated (such as color change, yellowing or whitening) after a long-time usage. Furthermore, it is also necessary for the protective film to have other characteristics such as good water resistance, chemical resistance, solvent resistance, acid resistance, alkaline resistance and the like.
Additionally, for the prior art, in a color LCD in order to maintain a constant layer distance (e.g. intercellular space) between two substrates, polystyrene beads or silica beads, for example, are randomly sprayed on the whole substrate, in which the diameters of these beads are equal to the distance between the two substrates. However, since those sprayed beads are uneven in their positions and distribution density by the prior methods, the light from the backlight source is scattered due to the influence of the sprayed beads, and thus the contrast ratio of the display devices are further reduced. For the aforementioned reasons, a photosensitive composition used for a spacer has been developed by photolithography and it has become the mainstream of the industry. At first, the photosensitive composition used for the spacer is coated onto the substrate, and then a light mask with a specific shape is placed between the substrate and an exposure source, followed by being exposed and developed, so that a spacer can be formed. Based on the aforementioned method, the spacer can be formed on given positions except R, G and B pixels, so as to solve the problem of the prior art. The cell gap can also be controlled by the thickness of the coated photosensitive composition, so that the distance of the cell gap can be easily controlled with the advantage of high precision.
Since the protective film or the spacer is formed on the color light filter or the substrate, the requirement for its transparency is extremely high. When such a protective film or spacer with poor transparency is used in the LCD, the brightness of the LCD will be insufficient, thereby affecting the display quality of the LCD.
In order to improve the transparency of the protective film or spacer, a photosensitive composition used for the protective film is disclosed in the Japanese Patent Laid-Open Publication No. 2010-054561, which includes an alkali-soluble binder resin (A); a compound (B) containing vinyl unsaturated group(s); a photoinitiator (C); and a solvent (D). The combination equivalent weight of the unsaturated bonds in the compound (B) containing vinyl unsaturated group(s) is 90 to 450 g/eq, the number of unsaturated double bonds in one molecule of the compound (B) containing vinyl unsaturated group(s) is 2 to 4, and the weight-average molecular weight of the alkali-soluble binder resin (A) is 10,000 to 20,000. Additionally, a photosensitive composition is disclosed in the Japanese Patent Laid-Open Publication No. 2004-240241, which includes (A) a copolymer (A) of an ethylenically unsaturated carboxylic acid (anhydride), an ethylenically unsaturated compound containing an epoxy group(s), and other ethylenically unsaturated compounds; (B) a polymerizable compound having an ethylenically unsaturated group(s); and (C) a photopolymerization initiator represented by 2-butanedione-[4-(methylthio)phenyl]-2-(O-oxime acetate), 1,2-butanedione-1-(4-morpholinylphenyl)-2-(O-benzoyloxime), 1,2-octanedione-1-[4-(phenylthio)phenyl]-2-[O-(4-methylbenzoyl)oxime] or the like. However, although such a photosensitive composition can be used to manufacture a protective film or spacer with high transparency, the photosensitive composition has disadvantages of poor resolution and development adherence.
Accordingly, it is necessary to develop a photosensitive resin composition used for a spacer or protective film with excellent resolution and development adherence, so as to solve various aforementioned problems of the conventional protective film or spacer.